﻿C Y U E X A. 



Genus CTRENA. Lamarck. 



^loi.i.rscrM ArEPHAi.OPODUM, biimisculosum.Jlun'aflle vel 

 suhjluviatilc. Testa cequivnhv's, iiirrquilateralis, 

 crassn, plus minusve nrliii-i'hin'^, finiiida, rnn- 

 rentr'tfe sulcata, vel ruijulii, tjii'/i riaide conied, 

 solkld indiitd; cardiiie cras.m, dentihi(,s cardinali- 

 biis diwhus aut trihus, lateralibics elo>igati.9, nonnun- 

 qiinm, striatis ; pallii innyressiono iiitrgrd, vel vix 

 slnioijd. 



^lor.LrsKACEi'HALOPODOus.bimnscnlar.fluviatileorsub- 

 fluviatile. Shell ciiuivalve, inequilateral, thick, 

 more or less orbicular, tumid, concentrically 

 grooved or wrinkled, covered with a horny 

 solid epidermis ; hinge thick, cardinal teeth two 

 or three, lateral elongated, sometimes striated ; 

 pallcal impression entire, or very slightly 

 sinnatiid. 



Tlic shells composing this genus inhabit rivers and 

 estuaries in tropical America, India, China, Austra- 

 lia, the Philippines and Islands of the Pacific. 

 Although principally of freshwater habits, some 

 are found in brackish water, and in tht; mud of 

 mangrove swamps. 



The distinctions between Corhicida, Batissa, and 

 Cijrena seeming to me scarcely of generic importance, 

 I have united them in this work under one generic 

 term. It may, however, be convenient in the fol- 

 lowing list of specific numbers to designate the 

 Section to which each species belongs : — 



Section 1. Batissa. Lateral teeth straight and of 

 moderate length. Species 1-21, 28. 



Section 2. Cokbicula. Lateral teeth long, curved, 

 and angular. Species 45—18, ol-Gl, 66-70, 72-77, 

 79-101. 



Section :^. Cyrexa. 22-27, 20-1-1, 40, 50, 62-65, 

 68, 71, 78, 102-114. 



Species 1. (Mus. Brit.) 



Ctrexa GIGAXTEA. Ci/r. testa mat/nd, pondcroyd.. .-■/.?/. 

 ovatd, valda inreqnilaterali, {rrcrjularifer yiilciild, 

 epidennide cragsd, nigra iitdnfd ,- /////'/x ,(//,,(, 

 incrassatd, piartim purpurea litirtd ; latin' nultf,' 

 hrevi, postico producto, oLsnirlay/'nie (iiiijiihitu ; 

 cardine lato,dentihiis cardinal liny iufryriy, ht'irtdl 

 antico hrevi ; ligamento magno, eloiigata. 



The gigantic Ctrena. Shell large, ponderous, rather 

 oval, very inequilateral, irregularly grooved, 

 covered with a thick black epidermis ; interior 

 white, thick, tinted in parts with purple ; 

 anterior side short, posterior produced, vei-y 

 obscurely angular ; hinge broad, cardinal tooth 

 entii-o, anterior lateral short ; ligament largo, 

 long. 



Prime. MS. Brit. Mus. 



Hah. Philippines ? 



This species, having a short lateral tooth in front, 



is not very characteristic of the first or Ilat(ss<i 



section. 



Species 2. (Mus. Brit.) 



Cyrexa lenticularis. Cyr. testa rotutidd, lenticnlari, 

 alia, siiLceqiiilaterali, irrcgnlariter riigafii, e/ii- 

 dermlde solidd,snhru-iih\ „;ir„i; nnlntd, ;„t,)yferr 

 omninli imrpiir<-n rli-i,l,t snljnsd ; c.irdiin' yi'lmn- 

 gmin, dente an-dinnU cnlndl hijidn, latenillhny 

 O'qualiter elongatis, comq)ressi.s, tenuissimeserralis. 



The lenticular Cyrena. Shell rounded, lenticular, 

 high, subequilateral, irregularly wrinkled, 

 covered with a solid rather green epidermis, 

 suffused within nearly all over with vivid purple ; 

 hinge rather narrow, central cardinal tooth 

 bifid, lateral equally elongated, compressod, vory 

 finely striated. 



Deshates. Proc. Zool. Soc. 1854. 



Hah. Philippines. 



